Silica-containing anionic microparticles are used as part of retention and dewatering programs in the production of paper and board products. In the paper making process, these particles are added to the flowing stock containing cellulose fibers, fillers, clays, dyes, starches, coagulants, anionic trash catchers (ATC's) and other additives, either before or after the addition point of a high molecular weight flocculant. Before products comprising the silica-containing anionic particles are added to the stock, the product is diluted with process or fresh water. This dilution may be on a volume basis and can range from about 25 to about 200-fold, i.e. one gallon of silica-containing anionic microparticle-containing product may be mixed with from 25 to 200 gallons of water.
It is known that silica-containing anionic microparticles can gel or precipitate as a result of this dilution depending on the hardness of the dilution water. This gelation or precipitation of the microparticle results in reduced retention and dewatering performance thereby requiring higher dosages and correspondingly increased material costs to achieve the desired level of performance. Production may also be interrupted in order to remove gel from the piping and dilution system. Fluctuations in the dilution water quality can also lead to variation in program performance and product quality as a result of swings in retention and drainage. In order to obviate the foregoing problems, producers have been forced to employ costly water treatment to reduce water hardness prior to use as a diluent for silica-containing anionic microparticle products. Accordingly, there is an ongoing need for compositions and methods for stabilizing silica-containing anionic microparticles against gelation or precipitation where hard water must be used in papermaking processes.